The idea of getting to know the puppeteer responsible for the yellow-feathered sweetness of "Sesame Street's" Big Bird is a bit scary. After all, as we learned in "The Wizard of Oz," looking behind the curtain can be very disappointing.

Have no fear. Dave LaMattina and Chad N. Walker's "I Am Big Bird: The Caroll Spinney Story" is the kind of heartwarming, sentimental tale of a gentle soul that the PBS show's iconic character would love.

As we learn from the start, bringing Big Bird to life has always been an inside job, one that Spinney has done for 45 years. It is interesting to see the process of melding the two together: Spinney pulling on those bird legs like trousers; getting wired for sight and sound — there are no hidden peepholes; Spinney navigates by looking at a tiny screen in front of him — then slipping on that giant body, his right arm extending up the neck, his hand moving the mouth in much the same way a kid manipulates a sock puppet.

That Spinney is now 80 and not interested in hanging up his feathers gives you a sense of how much the character has meant to him. As he talks, in present-day interviews and in archived footage — both public and private — what emerges is an extraordinary bond between man and, um, beast. Spinney is also responsible for the growling impatience of Oscar the Grouch, but Big Bird is clearly still No. 1 in his book.

From the beginning, the filmmakers promise an affectionate look at the man, and in that they deliver. There are a few references to Spinney being bullied as a child. And there are passing references to his first marriage that produced three children and ended in divorce.

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Spinney's kids speak of their father and the character that took up much of his time and attention with affection as well. If there is any of the resentment Candice Bergen had for her father's puppet Charlie McCarthy, none of it makes it into this film.

Besides Big Bird, the most important relationship in Spinney's life is that with his second wife, Debra. Their marriage in 1979 brought Spinney not only a wife but also a constant companion — always at his side.

Beyond the mechanics of bringing Big Bird to life, the documentary also traces the puppet's trajectory from obscurity to superstardom, with Spinney along for the ride, from the trip to the Great Wall of China to the near-miss of being on the ill-fated space shuttle Challenger, whose educator slot was initially to be filled by Big Bird. Intercut are interviews with many of the other producers and artists working in this very specialized world.

'I Am Big Bird'

Debra Spinney / Tribeca Film

A photo of Caroll Spinney and Snuffleupagus on the set of "Sesame Street" in the movie "I Am Big Bird."

A photo of Caroll Spinney and Snuffleupagus on the set of "Sesame Street" in the movie "I Am Big Bird."

(Debra Spinney / Tribeca Film)

But the film is at its best when Spinney remembers the past as clips of Big Bird fill the screen. For so many who grew up watching "Sesame Street," and then watched with their children, it becomes a little like flipping through an old friend's scrapbook.

Not surprisingly, Spinney was very close to Muppets creator Jim Henson, who until his death portrayed Kermit the Frog. One of the most moving moments comes in footage from Henson's funeral with Big Bird's elegy to his lost friend.

In a sense, it seems fitting that "I Am Big Bird" is a modest project driven more by good intentions than great artistry. Both the man and the Muppet at its center are self-deprecating, which makes peeking behind the curtain not scary at all.